Vacuum tube



July 19,1927.

H. E. METCALF VACUUM TUBE Filed Oct. 13, .1924

Jitter-naps;

Patented July 19, 1927.

UNITED STATES 1,636,239 v PATENT OFFICE.

HERBERT E. METCALF, OF SAN LEANDRO, CALIFORNIA, ASSIGNOR TO THE KAGNAVOI COMPANY, OF OAKLAND, CALIFORNIA, 'A CORPORATION OF ARIZONA.

VACUUM TUBE.

Application filed October 13, 1924. Serial No. 743,388.

This invention relates to radio vacuum tubes of the three-electrode type for use as rectifiers, amplifiers and electric wave generators, and more especially to that type of.

' I three-electrode tube described by me in a co-pending application filed March 23, 1925, Serial No. 17,580, wherein the third or control electrode is in the form of a slotted conductor with the cathode placed within the slot.

The object of the invention is to improve the construction of such a device whereby it is made incapable of generating the so- -called microphonic noises to which all such devices are more or less subject, and whereby extreme resistance to external shocks is obtained along with permanent alignment of internal electrodes even in the face of strong external shocks.

In investigating the cause of the internal noises'of such a tube, I have found that while noises appearing in the output circuit of the device are small, nevertheless when the device is used as a detector of electric waves, and the output amplified. the

noises are objectionable. On further investigation, I have found that while the causes of these microphonic noises are varied. by far the greatest amount of microphonic noise or sing is due to a definite period of vibration taking place in the filament. The device commonly used with practically all three-electrode tubes will, when lightly tapped or subjected to slight shocks, cause a microphonic noise or sound in the output circuit. Inasmuch as the noise has been found to be due to periodical vibration of the filament. thereby changing its position relative to the other electrodes contained therein, my present invention deals with a new construction whereby this periodical vibration is dampened and killed, and the usual microphonic noises in the output circuit of three-electrode vacuum tubes eliminated.

It is well known that a wire or other filamentary substance will, particularly when supported by springs, vibrate with a certain frequency depending on various factors. In 50 my investigation of the cause of microphonic noises in vacuum tubes, I have demonstrated the fact that the filament, supported as it usually is by aspring to take up expansion under heat, vibrates to a great extent and that the period of vibration corresponds to the electrical variations in the output circuit and causes the microphonic noises. By stopping this riodic vibration ofthe filament, the noises in the output circu1t are also stopped. In accordance with my invention, I stop this vibration. by placmg a damper, similar in its action to that of a damper on a piano string, on the filament intermediate the ends thereof.

Another object of my invention is to provide an improved three-electrode vacuum tube in which the said objectionable noises are eliminated by dampening the filament in the manner stated.

Referring to the figures of the drawing:

Fig. 1 is a side elevation of a vacuum tube constructed in accordance with my invention, parts of the bulb being broken away for the sake of clearness.

Fig. 2 is a sectional view thereof taken on line 22o'f Fig. 1.

Fig. 3 is an enlarged detail view of the filament and its supporting means shown in Fig. 1'; this view eing at right angles to that shown in Fig. 1.

Fig. 4 is a view similar to Fig. 1 showing my invention applied to another form of vacuum tube.

Fig. 5 is a sectional view thereof taken on line 5-5 of Fig. 4.

Fig. 6 is a fragmentary view illustrating one of the objects to be accomplished by my invention.

Referring to Figs. 1, 2, and 3 of the drawing, 1 indicates a vacuum tube having mounted therein two plates'A and A, a filament B, and a control electrode C. The plates, which are connected together as shown inmy aforesaid application, the 'filament, and the control element constitute the three electrodes of the tube. In the particular form illustrated in Fig. 1, the control electrode C is in the nature of a triangular shaped metallic plate, and the filament is carried in a V-shaped slot formed in this 109 plate, the filament being supported at its apex by means of a spring arm 2 projecting out from a standard 3.

As illustrated, the two ends of the filament B, are supported at 4, and the apex 105 thereof is supported by the spring arm 2. Ordinarily, when supported in this manner, the filament will vibrate intermediate its supports, as indicated diagrammatically in Fig. 6, and cause the ob ectionable noises 110 above referred to. In'accordance with my aeeaaae tion applied to the grid type of three-elecinvention, I provide means in constant en-b trode tube. In this construction, the tube 7 gagement with the intermediate portion of the filament for preventing this vibration.

If the filament is in the form of a V, as illustrated in the drawing, adamper should be placed on both legs thereof. This damper may be made of a non-conductor, or if of a conductor, it should be insulated by some non-conductor from the other electrodes. I prefer to make this damper out of a thin narrow strip of mica, or other suitable material, held in place by suitable supports on the control electrode 0.

In Figs. 1, 2, and 3, I have shown two pieces 5 and 6 of mica used as dampers for the filament B" These dampers are mounted on thecontrol element C, one adjacent the apex of the filament, and the other midway between the first damper and the filament supporting point 4. The dampers, both of which preferably pass between the legs of the filament, are preferably so arranged that one leg of the filament passes over the damper 5 and under the damper 6, thence over the spring arm 2, then on the opposite side of the damper 6, and from thence under the damperh. This method makes certain that the filament will always be in contact with the mica, because of the pull of the spring arm 2 which tends to straighten out the filament. Such a construction rforms the dampening operation by touc ing the filament and still allows the slack due to the expansion of the filament under heat, to be taken up by the s ring arm 2. This is due to the fact that t e filament may slip over the mica, or other damper material provided. It should be understoodthat my mvention is alsoapplicable to the three electrode vacuum tubes other than above described. In Figs. 4 and 5, I have illustrated my invenhas mounted therein two plates a and a, a. filament b, and the usual form of grid 0. The filament is supported within the grid in a manner similar to that described in reference to Fig. 1. A pair of mica plates 8 and 9 are supported on the grid, extend between the two legs of the filament, and touch the opposite sides of the filament in the manner above described.

It is believed that my invention and its various advantages will be clearly understood without further description thereof, the main objects accomplished being the dampening of the filament. to prevent vibration thereof and the objectionable microphonic noises, and the more rigid supporting of the filament in place whereby the same is less liable to be displaced or become. broken. It should be clearly understood, however, that while I have herein illustrated and described certain detailed embodiments of my invention, the invention can be otherwise em bodied within the scope of the appended claim.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

A radio vacuum tube of the character described having a-plurality of electrodes therein, a V-shaped filament adjacent one of the electrodes, and a pair of elements extending between and dampening vibration of the two legs of the filament by touching the same between the ends thereof, one of the elements being adjacent the apex of the filament and touching one side of each leg thereof, and the other element being spaced therefrom and touching another side of each leg.

HERBERT E. METOALF. 

